-   irv 


Circular  No.  66,  Revised  Edition. 


I 


I  oited  States  Department  of  Agriculture, 


BUKKAU  OF  BNTOMOLO 

Entomologiiit  and  Cli 


J0INT-W01 

i  !i<  h  i 

I       M      WSBBTl  i: 

m!  Forage  Plant  l 

since  the  first  known  Berious  outbreak  of  the  joint-worm  (Isosoma 
tritici  Pitch),  which  occurred  in  the  wheal  fields  about  Charlottesville 
and  Gordonsville,  Va.,  during  the  years  1848  to  1854,  this  insecl  has 
been  reported  ;it  irregular  in  ten  alsand  from*  idely  separated  localities. 
While  it  i-  known  to  occur  sparingly  over  most  of  the  wheat-growing 
sections  of  both  the  United  State-  and  Canada,  and  probably  <l 
more  damage  than  has  generally  been  attributed  to  it.  it-  reappear- 
ance in  tlic  wheat   fields  of  Indiana,  Michigan,  Ohio,  Pennsylvania, 


r,|). 

West  Virginia,  Virginia,  Maryland,  and  Kansas  in  1904,  and  in  -till 
greater  numbers  in  1905,  Berves  to  bring  it  again  to  notice.  In  1904 
some  fields  of  wheat  in  eastern  Ohio  were  so  badly  damaged  that  they 
were  not  harvested,  and  in  tmi:,  a  serious  outbreak  in  northeastern 
Indiana  so  discouraged  some  fanner-  that  they  questioned  the  advisa- 
bility of  putting  in  a  crop  of  wheat  at  all.  In  southwestern  Virginia, 
the  pest  was  even  more  injurious  in  1905  than  it  was  the  previous  year. 
The  pest  w  a-  al-o  very  destructive  in  western  ( mioand  eastern  Indiana 
during  the  spring  of  1908. 
.:>_•  7 1  s    Cir.  Bl 


DESCRIPTION    OF   THE    PEST 


The  fully  developed  insect,  somewhat  resembling  a  small,  winged 
black  ant,  is  clearly  shown,  enlarged,  in  figure  1,  its  natural  size  being 
indicated  by  a  line  at  the  right.  The  color  is  black,  with  joints  of  legs 
and  feet  yellow.  The  larva  or  grub  is  whitish,  with  brown  jaws,  the 
length  being  about  the  same  as  that  of  the  adult,  and  the  form  much 
like  that  shown  in  figure  2,  which  represents  the  larva  of  a  nearly 
related  species. 

LIFE    HISTORY. 

The  insect  may  be  found  in  wheat  stems,  in  its  various  stages  of  devel- 
opment, throughout  the  year.     It  lives  through  the  winter  as  a  larva 

or  grub  in  cells  formed  in  the 
stems  prior  to  the  ripening  of 
the  grain,  the  adult  emerging 
therefrom  in  April  or  May,  ac- 
cording to 
latitude,  or 
some  time 
after  the 
young  grain 
has  thrown 
up  stems 
and  several 
joints  have 
become  ex- 
posed. The 
female,  us- 
ing her  slen- 
der, pointed 
oviposit  or, 
places  her 
eggs  in  the 

•    ■ 

stems.  The 
exact  posi- 
tion assum- 
ed is  shown 
in  figure   3, 

from  a    photograph   from   life 
by  Mr.  G.  I.  Reeves.      The  eggs 

Fig.  3.— Female  Isosoma  In  act  of  depositing  egg  in     hatch    and     the    young    grubs, 
stem.    About  lite  size  (author's  illustration).  formmg      (.ejj.s      feed       ill      the 

Avails  of  the  stem,  reaching  their  maximum  growth  by  the  time  the 
straw  becomes  fully  .  udened  and  ripe.  Wintering  in  the  larval 
state,  they  pass  a  short  pupal  stage  and  emerge  as  adults  in  the 
Spring.     While  there  are  both  males  and  females  among  these  insects. 

[Or.  LO] 


Fig.  2.— Isoxoma  grnndc 
Larva  of  the  wheat- 
straw  worm;  r,  anten- 
na; /.  jaw.  Line  at 
right  indicates  natural 
length.     (After  Riley.) 


8 


Mr.  Phillips  of  thifl  Bureau  has, 
during  two  successive  years,  found 
thai  "unfertilized  females  \\  ill  deposil 

ami  thai  these  eggs  \\  ill  hatch 
out  larvie  which  develop  to  adull 
insects.  It  is  pr< ibable,  how ever, 
thai  these  adults  w  ill  be  round  to  be 

■l\  01  till  males. 

iiiii  i   o\    i  hi    s 1 1;  \\v. 

The  effecl  on  the  straw  of  the  work 
of  the  joint- worm  is  exceedingly  vari- 
able. Sometimes  .1  distortion  occurs 
like  thai  illustrated  in  figure  I ;  a1 
other  times  the  straw  i->  benl  or 
twisted  iu  almosl  even  conceivable 
shape;  again,  there  will  be  no  enlarge- 
ment of  the  straw  whatever;  orthere 
nun  be  large  galls  or  excrescences,  as 
it  were,  bursting  oul  of  the  base  of 
tlu«  -heath  at  one  side,  some  of  these 
abnormal  growths  having  pseudo- 
rootlets  extending  downward  from 
their  lower  extremity.  Sometimes 
the  straw  will  make  about  normal 
grow  th  and  the  hardened  sections  will 
be  restricted  to  an  inch  or  there- 
abouts just  above  the  lower  joints; 
and, again, the  growth  \\  ill  nol  exceed 
:;  or  f  inches,  often  nol  heading  at 
all,  or  with  aborted  head  and  with 
the  straw  galled  or  hardened  to  the 
base  of  the  head.  In  some  oases 
there  is  no  outward  indication  of  at- 
t.-u  k  whatever,  the  affected  pari  be- 
ing \\  holly  inclosed  in  the  sheath,  and 
when  thislasl  is  removed  the  presence 
of  the  cells  i-  indicated  only  by  a 
slight  discoloration,  and  frequently 
by  a  few  small,  more  or  less  irregu- 
lar, elevated  ridges. 

In  thrashing  the  grain  the  hard- 
ened portions  of  the  straw,  as  shown 
in  figure  5,  break  up  into  pieces  of 
from  halt  an  inch  to  an  inch  or  more 

[dr.  06] 


in  length,  many  of  which  do  no!  go  over  with  the  straw  and  chaff, 
but  remain  with  the  grain.  The  presence  of  these  bits  of  broken  straw 
in  the  grain  is  frequently  the  first  evidence  the  farmer  has  seen  of  the 
occurrence  of  the  pest  in  his  fields.  Millers  and  elevator  men  note 
them  also,  and  in  sections  where  the  pest  has  committed  serious  dep- 
redations several  bushels  of  these  hardened  bits  of  straw  are  found 
after  each  day's  cleaning  of  the  grain. 

EFFECTS    OX    THE    KERNEL. 

The  wheat  heads  from  infested  stems  are  foreshortened,  and  the 
kernels  thereby  necessarily  reduced  in  both  size  and  number,  and  in 
case  of  severe  attack  they  become  shrunken. 


NATURAL    ENEMIES. 

Natural  enemies  of  the  joint-worm  are  quite  numerous,  and 
most  of  them  have  the  advantage  of  being  double-brooded,  whereas 

the  joint- worm  has  but  one  generation 
annually. 

Among  the  most  efficient  of  these  are 
two  rather  common  species  of  insects. 
One  of  these,  almost  as  big  as  the  Isosoma 
itself,  with  dull  metallic  thorax  and  yel- 
low abdomen  and  with  long  ovipositor, 
is  Ditropinotus  aureovirid'ts  Crawford,  and 
the  other,  smaller,  darker  colored,  and 
slender,  also  somewhat  resembling  an 
Isosoma,  is  Eupelrnus  allynii  French. 
The  writer  reared  also  another  species  in 
Ohio,  Websterellus  tritici  Ashm.,  which  has 
similar  habits. 

A  somewhat  similar  insect  with  metal- 
lic body  and  yellow  abdomen,  Stictonotus 
isosomatis  Riley,  is  very  efficient  in  destroy- 
ing the  larva1  in  the  straw.  Homoporus 
(Semiotdlus)  chalcidijihagus  Walsh  and 
Riley,  and  beyond  a  doubt  other  chalcidoids,  are  also  instrumental  in 
holding  the  pest  in  check.  These  are  all  small  four-winged  flies,  and 
a  number  of  additional,  undescribed  forms  have  been  discovered. 

The  larva  of  a  small,  slender,  black  and  yellow  carabid  beetle  (Lepto- 
trachelus  dorsalis  Fab.)  crawls  up,  descends  into  the  stubble,  and  de- 
vours the  Isosoma  larvae,  but  unfortunately  its  sense  of  taste  seems  to 
be  too  obtuse  to  allow  it  to  confine  itself  strictly  to  Isosoma,  and  as  a 
consequence  it  devours  parasites  as  well  as  host.  A  mite,  Pedicu- 
loides  (Hetoro'pus)  ventricosus  Newp.,  is  also  an  enemy,  gaining  access 
to  the  larvae  precisely  as  does  the  beetle  larva  previously  mentioned. 

[Cir.  66] 


Fig.  5.— Bits  of  hardened  straw  re 
maining  with  the  grain  after  thrash 
ing.     (Author's  illustration.) 


I-Kl  \  I  \  I  l\  I      mi    \-i   1:1 

There  are  no  known  remedies  for  the  joint-worm,  but  there  are 
several  preventive  measures  t  lmt  are  not  impracticable  and  are 
reasonably  efficient . 

In  the  nudsl  of  tin-  outbreak  in  Virginia,  previoualj  mentioned,  a 
'Joint-worm  Convention"  was  held  at  Warrenton,  in  that  State,  to 
devise  means  for  controlling  tlii-  pest.  ' I " 1 1 i  —  bod}  recommended  a 
better  system  of  farming,  the  use  of  guano  and  other  fertilizers  to  pro- 
mote a  rapid  grow  th  and  an  earl)  ripening  of  the  grain,  and  the  burning 
of  the  si  iil>l>l»\  nil  of  \\  1 1 irli  arc  as  n<\\  isable  tt)-tla\  as  thej  were  at  thai 
time.  The  nu>--t  serious  ia\  ages  are  observed  on  thin  <>i-  impoverished 
soils,  especially  along  the  margins  of  the  fields  infested.  Anything, 
then,  that  tends  to  add  vigor  to  the  young  grow  inur  grain  will  constitute 
a  |>iv\  entive  measure.  Burning  t  In-  st  ubble,  \\  here  i  his  i-  pract  icable, 
is,  of  course,  most  efficacious,  but  over  the  larger  portion  of  the  terri- 
torj  ravaged  by  this  pesl  it  is  customary  to  seed  with  grass  after 
wheat,  and  under  this  condition  burning  over  the  Btubble  field  is 
impossible.  Such  fields  should  be  raked  over  with  an  ordinary  hay 
rake,  and  the  loosened  stubble  removed  and  burned  before  the  adults 
have  emerged  in  the  spring.  It',  however,  the  grain  is  cul  low  at 
harvest,  and  the  straw  passed  through  the  stables  as  bedding  for 
Btock  during  the  winter,  tlm>  becoming  saturated  by  liquids  and  more 
or  less  thoroughly  composted,  the  treatment  would  seem  sufficient  to 
destroy  the  [sosoma  larva?  so  thai  few,  if  any.  would  develop  adults 
tht"  following  spring.  In  case  t>f  bedding  for  horses,  it  seem-  quite 
probable  thai  if  an\  larvae  at  all  survived  the  thrashing  machine,  the 
heat  from  the  decomposing  manure  would  develop  them  prematurely. 
However,  there  has  been  nn  experimentation  exactly  along  these 
lines,  and  according  to  a  press  bulletin  by  Prof.  K.  II.  IVttit,  of 
the  Michigan  Agricultural  College,  serious  injuries  have  followed  the 
year  after  application  and  plowing  under  of  barnyard  manure  in  the 
fall  before  the  wheat  was  sown.  In  this  case  the  manure  would 
necessarily  be  fresh  and  the  bedding  t»f  straw  t>f  the  same  season's 
growth,  otherwise  the  adults  would  have  already  emerged.  This 
would  be  a  proposition  quite  different  from  that  of  allowing  the  stable 
manure  to  accumulate  during  t  he  winter  ami  applying  it  in  the  spring 
elsewhere  than  to  the  wheat  fields,  <>r  even  of  applying  it  to  wheat 
fields  before  plowing,  months  after  the  larva  surviving  the  effects  of 
the  stable  had  developed  and  escaped.  The  one  might  destroy  all  or 
nearly  all  larva'  in  the  straw,  ami  the  survivors  would  emerge  about 
the  .-tables  or  in  the  barn  van  I :  while  the  other  met  hot  I.  -imply  to  take 
the  straw  with  the  living  larvae  present  from  an   old  field,  mov< 


■■  Mi.-li.  A.  ip.  S        P  l">.     The  Wheat  Joint-Worm. 


through  the  stable,  cart   it  out  on  a  new  field,  and  plow  it  under,  is 
one  that  the  fanner  should  evidently  be  careful  to  avoid. 

Exactly  in  this  connection,  an  assistant,  Mr.  Charles  N.  Ainslie, 
while  waiting  between  trains  in  the  city  of  St.  Louis,  Mo.,  found 
at  the  corner  of  Sixteenth  and  Locust  street-  a  pile  of  bricks  to  be 
used  in  the  erection  of  a  building.  These  bricks  were  stamped  "MftS- 
sillon,  Ohio,''  and  were  packed  in  straw  which  the  chief  contractor 
stated  came  with  the  bricks  from  Ohio.  This  straw  contained  larvae 
of  this  species  which  later  on  transformed  to  adults,  but  the  latter 
did  not  emerge  from  the  straw. 

In  the  past  it  has  always  been  thought  necessary,  as  a  precautionary 
measure,  to  burn  the  infested  bits  of  hardened  straw  that  break  up 

in  thrashing  the  wheat,  many 
being  carried  out  with  the 
grain  instead  of  going  over  in 
the  straw.  Several  experi- 
ments in  rearing  adults  from 
large  numbers  of  these  broken 
bits  of  straw  (fig.  5),  collected 
about  elevators  and  thrash- 
f/,  '.*  ,«  i  |\  Vl  71!       ing  machines,  has  shown  that 

almost  all  of  the  larvae  of 
both  Isosoma  and  parasites 
are  killed,  probably  by  the 
concussion  of  the  cylinder  of 
the  thrasher.  In  some  cases 
we  have  been  able  to  verify 
these  experiments  by  collec- 
tions of  stubble  from  fields 
in  the  vicinity  of  these  ele- 
vators. So  far  as  we  have 
gone  into  the  investigation 
everything  indicates  that  the 
danger  from  these  broken  bits  of  hardened  straw,  or  even  from  t  he  st  ra  w 
itself,  is  of  too  little  importance  to  be  worth  consideration.  Prof.  R.  H. 
Pettit,  of  the  Michigan  Agricultural  College,  and  Mr.  W.  J.  Phillips,  of 
this  Bureau,  in  1906,  found  in  northern  Indiana  great  numbers  of 
straws  affected  by  the  joint-worm,  where  the  enveloping  sheath  had 
been  torn  away,  the  galls  formed  by  the  larva'  deftly  eaten  away,  and 
the  joint-worms  missing.  In  no  case  was  the  entire  gall  gnawed  aw  ay, 
but  just  enough  of  the  walls  immediately  over  the  larva  to  make  pos- 
sible the  removal  of  t  he  latter  (fig.  6).  While  we  have  not  been  able  to 
get  definite  information  as  to  the  identity  of  this  decidedly  beneficial 
animal,  suspicion  seems  to  point  to  the  short-tail  shrew   (Blariita' 

[Cir.  1.'.] 


Fig.  0.— Wheat  straws  injured  by  the  joint-worm 
(Isosoma  tritici),  from  which  the  joint-worms  have 
been  removed  by  some  beneficial  animal,  perhaps  the 
short -tail  shrew  (Blarina  breiicauda).  (Author's  illus- 
tration.) 


icauda)  as  the  species  to  which  credil  Bhould  be  given,  and  prob- 
al,|,   much  of  the  work  is  done  while  the  grain  is  in  shock. 

Rotation  of  nop-,  is  advantageous,  because  il  necessitates  the 
migration  of  adults  from  one  field  to  another,  and  if  this  takes  place  in 
stormy  weather  or  during  high  winds,  manj  of  the  migrants  will  be 
killed  or  blown  astray.  Il  is  easily  Been  thai  where  infested  strav  is 
applied  to  a  aev.  field  prior  to  Bowing  to  wheat,  this  migration  of 
adults  would  not  be  made  oecessarj . 

The  Bowing  of  early  ripening  varii  ties  is  also  beneficial. 

Approved : 

.1  Lit  ES    WlLS<  )\  . 

Secretary  of  Agriculture. 
Washington,  D.  C,  July  16,  1908. 

|CU 

O 


UNIVERSITY  OF  FLORIDA 

3  1262  09216  4507 


